Linear copolyesters have been produced heretofore for various purposes, particularly for the production of films and fibers, but the known polymers of this type have not been as effective as would be desired for certain applications. In particular, certain polymers of this type did not possess superior tear strength, flex life, abrasion resistance and rapid hardening rates which would be required for many uses such as hydraulic hose and cable coverings. Recently, copolyetheresters have been discovered which possess such properties. Although these copolyetheresters are significantly superior to those previously known in the art, in many regards, they have presented a problem with regard to resistance of the polyether backbone toward oxidative degradation. That is to say, with prolonged exposure to temperatures above about 120.degree.C. or sunlight the copolyetherester has tended to degrade. For many applications requiring good heat aging or weathering characteristics there has been a need for a high performance thermoplastic elastomer combining rapid hardening rates with superior resistance toward oxidative degradation.